The long term objective of this research is to understand the molecular mechanisms regulating chemotaxis during terminal branch outgrowth in the tracheal system of Drosophila. The directed outgrowth of these cells is controlled by an attractive guidance signal originating from oxygen-starved target tissues. This is similar to the development of other epithelial tubes, such as the mammalian vascular system, in which the capillaries also develop in response to the oxygen needs of their target tissues. Therefore, the molecular characterization of the gene misguided, which has misrouted terminal branches, as well as the identification of other genes affecting the directed outgrowth of these cells will help elucidate the molecular mechanisms controlling terminal cell outgrowth. In the long term, this type of molecular genetic approach will hopefully identify the tracheogenic signals originating from the target issues, lead to a greater understanding of the role of oxygen in regulating these signals, determine the manner in which these signals are communicated to and transduced by the terminal cells, and elucidate the cellular mechanisms used during cytoplasmic outgrowth of the terminal branches. Studying how the physiological requirements of the target tissues are coupled to the development of the terminal cells in Drosophila will also lead to a molecular understanding of this process in other systems that are less amenable to molecular genetics.